Applicant claims priority under 35 U.S.C. xc2xa7119 of German Application No. 100 16 006.9 filed on Mar. 31, 2000.
1. Field of the Invention
The invention concerns a filter device to be connected to a conduit for microfiltration and/or ultrafiltration, preferably for varnishes, such as cathodic dipping varnishes, having a pressure housing and at least one ceramic membrane filter element located in the pressure housing. The present invention further concerns a process for microfiltration and/or ultrafiltration of fluids to be filtered using at least one filter device of the type previously described.
2. The Prior Art
In practice, filter devices for microfiltration and ultrafiltration of the type initially mentioned are used in many areas. Areas of use are, for example, the filtration of waste water, cleaning solutions, cooling lubricants as from drilling emulsions, and cell separations in high load biology, the concentration of brick engobes, the cleaning of pickling baths, as well as the recycling of swimming pool water. Filter devices of the type initially mentioned are also used in the chemical and biochemical industries for cell separation, protein filtration, dye filtration, catalyst reclamation, and purification of photochemical developing solutions. Furthermore, these types of filter devices are also used in the food industry, for example, in the filtration of sediment from beer, in the clarifying filtration of sugar syrup, fruit juice, wine, and vinegar, in the defatting of whey, and in lactoferrin filtration.
Filter devices of the type initially mentioned are not typically used in the area of varnish recycling, particularly of cathodic dipping varnishes which are used in the varnishing of motor vehicle parts. This is because it has become known that ceramic membrane filter elements clog relatively quickly, so that economical recycling of varnish with filter devices of the type under discussion is currently not possible. For these reasons, filter devices with polymer filters are typically currently used for the recycling of cathodic dipping varnishes.
However, it is problematic that polymer filters have a comparatively low operational capacity when used for the recycling of cathodic dipping varnishes. Due to the comparatively low operational capacity, very large filter areas are required to be able to process large amounts of fluids to be filtered and/or recycled, which, in turn, requires a relatively large amount of space for a polymer filter facility. A further disadvantage of polymer filter devices when used for cathodic dipping varnish recycling is that the polymer filter elements have a comparatively short service life of between half a year and a year. The polymer filter elements must subsequently be replaced, which requires a corresponding expenditure of work. Furthermore, when polymer filter elements are used in the way described, the polymer filters must be cleaned after shutting down the filter installation for operational reasons, in order to achieve the desired filtration capacity when the installation is started up again. These types of cleanings require increased expenditure of work and time, which is disadvantageous in regard to costs. If cleanings are not performed frequently enough or cleaning is unintentionally forgotten, the function of the entire installation can be significantly impaired.
An object of the current invention is therefore to provide a filter device of the type initially mentioned which is also suitable for the recycling of varnishes, particularly cathodic dipping varnishes.
The previously described object is essentially achieved, according to the invention, by a filter device of the type mentioned initially, in that a ceramic membrane filter element is electrically connected with at least one electrical conductor and is grounded via the electrical conductor. According to the method, it is provided that the fluid to be filtered is at least partially discharged before and/or during the filtration.
Surprisingly, it has been determined that, in the application of the invention, it is possible to recycle cathodic dipping varnishes economically with ceramic membrane filter elements without anything further being necessary. Other fluids having a charged state during filtration can also henceforth be filtered and/or recycled. The result according to the invention was surprising because the previous impression was that filter devices were, in practice, always grounded in any case. However, it has been determined using precise tests that, due to the nonconducting seals and buffers used, the pressure housings of the individual filter devices do not have sufficient grounding in and of themselves. Even with sufficient grounding of the pressure housing alone, the effect according to the invention could not be detected to the same degree occurring when the individual ceramic membrane filter elements are grounded. It is inferred from this that the effect according to the invention, namely the conductance of charges via the grounding, must occur directly at the location at which the filtration also occurs, namely at the ceramic membrane filter element itself. Furthermore, it is inferred from this that conductance of charges possibly present on the membrane surface of the ceramic membrane filter element itself also occurs due to the implementation according to the invention. In any case, the conductance of charges through the grounding of the ceramic membrane filter element keeps the individual molecules and/or ions of the fluid to be filtered from accumulating on the surface of the ceramic membrane filter elements and clogging the filter element in this way.
The advantages achievable with the invention are, in any case, convincing. Due to the significantly higher operational capacity, filter devices with ceramic membrane filter elements, which require significantly less space for the same operational capacity, can now also be used where previously only polymer filters could be used. Furthermore, it has been determined that the invention makes it possible, without anything further, to lengthen the intervals between cleaning of the filter device according to the invention, and/or not perform any cleaning at all over a long period of time, without this having disadvantageous effects on the degree of effectiveness of the installation. In addition, when ceramic membrane filter elements of the type according to the invention are used, the installation can be immediately started up again after it is shut down, i.e. no stripping or cleaning must be performed, which also contributes to improvement of the operational and/or functional reliability of the installation.
In a structurally simple development according to the invention, the pressure housing and/or the conduit which is connected to the filter device consists of an electrically conductive material, while the ceramic membrane filter element is connected via the electrical conductor with the pressure housing and/or the conduit. The grounding then occurs via the pressure housing and/or the conduit. Basically, it is, of course, also possible to lead the conductor as such out of the pressure housing and ground it directly.
In a particularly simple development of the present invention, the conductor is formed as a component separate from the pressure housing, preferably a wire, which electrically connects the pressure housing and/or the conduit with the ceramic membrane filter element. The use of a wire represents a very simple and economical development of a conductor which can also be realized as a supplement to existing installations at low cost, without anything further being necessary.
Particularly good filtration results are realized in this respect if the conductor is inserted in a through hole of the ceramic membrane filter element and extends at least over essentially the entire length of the through hole. In this way, a conductance of charges over the entire length of the ceramic membrane filter element is possible. It is particularly favorable if the conductor is led completely through the through hole and is grounded on both ends, i.e. is electrically connected with the pressure housing and/or the conduit on both ends.
Pressure housings of the type under discussion typically have a central pressure housing part and a fitting on each end for connection to the conduit. It is advantageous in attaching the conductor to the pressure housing that the conductor be held between the respective fitting and the pressure housing part, in particular that it be clamped between them. Of course, it is also possible to hold the conductor between the pressure housing and the conduit at the appropriate connection point.
Ceramic membrane filter elements of the type under discussion can have one or a plurality of through openings depending on use. It has been determined that if a plurality of through openings are provided, it is sufficient for adequate conductance of charges when only one conductor is provided for the ceramic membrane filter element. This conductor is then favorably located in one of the middle through openings, particularly the central through opening, insofar as one is provided.
In order, on one hand, to achieve a secure attachment of the conductor to the ceramic membrane filter element, and, on the other hand, to ensure good conductance of the charges, the conductor is glued to the ceramic membrane filter element in the through opening via an electrically conductive adhesive. It has been shown to be particularly favorable in this respect that the electrically conductive adhesive extends over essentially the entire face of the ceramic membrane filter element. It is thereby ensured that the fluid flowing to the filter device has the possibility of charge conductance as soon as it meets the face of the ceramic membrane filter element. Furthermore, the arrangement of the adhesive layer also has a positive effect on the conductance of charges from the surface of the ceramic membrane filter element.
It is also practical in this respect that the electrically conductive adhesive extends into all of the through openings for a short distance (preferably a few centimeters), i.e. not only in the through opening in which the conductor is located, but also in all other through openings not having a conductor. This can be easily achieved in the manufacturing process by dipping the end of the ceramic membrane filter element into the electrically conductive adhesive.
Filter devices of the type under discussion can, in principle, have one or a plurality of ceramic membrane filter elements. If a plurality of ceramic membrane filter elements are provided, it is sufficient for each ceramic membrane filter element to only have one conductor. In their installed state, the individual conductors projecting out of the ceramic membrane filter elements are then preferably collected into one strand, andxe2x80x94as described abovexe2x80x94grounded, or, however, a further conductor which is appropriately grounded is used, connecting together all the conductors.
In an alternative implementation of the present invention, it is provided that the ceramic membrane filter element is allocated to a device for generation of electrical field in order to achieve an electrical discharge or charging of the fluid to be filtered. In this alternative according to the invention, the conductance of charges to the outside via grounding does not occur, rather a charge equalization of the fluid to be filtered is intentionally performed.
The further positive results of the invention indicated above are achieved in the same way with this charge equalization.
Because the charge equalization must occur before or at least during the filtration in order to prevent accumulation of charged particles of the fluid to be filtered on the ceramic membrane filter element, the device for generation of electrical field is either effective within the pressure housing or is connected in series directly to the pressure housing.
In a particularly simple development of the embodiment previously mentioned, only one electrode is provided which serves as a sacrificial electrode. In another development, two electrodes are provided which are connected with an energy source wherein the strength of the electrical field is able to be adjusted via a corresponding adjustment device. This is then done according to the use and/or the type of fluid to be filtered.